1. Field of the Invention
The present invention relates to a monitoring device to monitor, record, and report chain wear for entire lengths of conveyor chains, and more particularly, to a portable monitoring device which attaches to an "I" beam of a chain drive conveyor system, and which electronically monitors and measures the entire chain in nominal ten foot increments to determine the chain wear.
2. Summary of Related Art
Chain drive conveyor systems are used throughout industry to move production assemblies and parts throughout a production facility. A plurality of trollies or other fixtures are interlinked with the chain at specific intervals such that the trollies are pulled by the movement of the chain in the chain drive conveyor system. Production parts and subassemblies are connected to the trollies. The layout and speed of the chain drive conveyor system is designed such that the right part is delivered to the right work station at the desired time in the production process. In many heavy industries, such as automotive plants, the plants will have multiple chain drive systems.
The overall chain length in a chain drive conveyor system can range from several hundred feet to several miles of chain. The links in the chain are made from forged steel with link pins connecting the adjacent links. The links in the chain gradually wear out during normal operation, and one or more links will eventually fail. The rate of wear depends on a number of factors, including the quality of the forged steel, the configuration of the chain, the weight of the loaded trollies being moved along the path of the chain, and other similar factors.
The chain for a chain drive conveyor system is quite expensive, with most chains costing several hundreds of thousands of dollars. Maintaining an inventory of replacement chains can be very expensive. Although a chain drive generally has uniform wear, a failure of one link will cause a break in the chain and the shutdown of the total chain drive system. In many chain drive applications, such as in automotive plants, production downtime can cost hundreds of thousands of dollars in a relative short period of time. A chain drive cannot be easily replaced and must generally be done as part of a planned periods of maintenance when the production operations are not in operation.
Because the chain of the chain drive system is expensive, and because production downtime is expensive, production engineers and maintenance staff have developed maintenance programs to maximize the financial return on the chain drive system by determining the optimum time to replace the chain in a chain drive system. The chain life may vary from two to ten years, depending on the application, with most chains being replaced every five to six years. Defective chain or excessive pressure on the take drive of the system can cause premature failure.
A power transmission chain in a chain drive conveyor system is typically formed by alternating links of rods and plates connected at each end by a link pin. The rods include a center aperture used to secure a trolley which is driven along the length of the conveyor. The chain wears at the ends of the links at the pin connection as the chain is driven along the length of the conveyor. Many chains are lubricated in an effort to reduce chain wear which occurs during operation.
The links are sized such that the pin-to-pin measurements are a standard length, with the most common sizes for links being three inches, four inches, and six inches. In a new chain, a ten foot segment of chain would be formed by forty of the three inch links, thirty of the four inch links, or twenty of the six inch links, depending on which of the standard size chain links are used in the chain drive conveyor system.
The most prevalent means for monitoring chain wear of a chain drive conveyor system in industry today is to manually measure the length of one or more segments of the chain, the segment of chain being determined by the number of links which would constitute a ten foot segment of new chain (40, 30, or 20 links generally). When new, the nominal segment of chain would measure ten feet. As the chain wears, the length of the segment gradually increases as the pins wear into the outer ends of the links. The general rule of thumb in industry is that when the segment of chain reaches a length of ten feet, four inches, the chain is ready to break and should be replaced. The four inch increase in length is merely a general guideline for replacement purposes.
The manual system requires an individual to count the links and measure the distance with a tape measure. The typical maintenance program includes measuring one or two segments of the chain, which on a typical 2000 foot chain is less than a 1% sample. Measuring additional segments is possible, but is expensive and time consuming for the equipment engineers and maintenance staff to manually measure multiple segment. Marking one or more segments for repeat measurement is also possible, but it is often difficult to locate the mark when subsequent measurements are to be taken.
A situation which frequently arises is that the chain will be lengthened after the initial installation of the chain drive conveyor system due to a change in the path of the assembly operations. Instead of buying a new chain, the existing chain is lengthened by adding links to the chain. The additional links are either new links which have never been used or old links from a used chain. In either case, the wear condition of the additional links is not representative of the wear condition of the majority of the chain. The manual chain wear measurement techniques do not provide reliable monitoring of such a chain configuration.
Recording and tracking the results is also inconvenient when chain wear is measured manually. To gain a reasonable benefit from such information requires a commitment of the maintenance staff to log and track the results on a regular basis and to monitor trends in the wear of the chain links. Two individuals are typically needed to measure and write down information. The chain is covered with lubricants and is messy to work with and write down data. The initial data must then be logged or entered into a computer system to provide a usable history of the chain wear condition.